The present invention relates to an apparatus for modeling a skeletal structure before and after a surgical procedure is performed on the structure. More particularly, it relates to a tool that may be used to model the structure and mechanics of a skeletal joint both before and after an osteotomy is performed on a bone of the joint.
Many medical conditions involving the skeletal system may be remedied by the performance of an osteotomy technique, or the surgical division or sectioning of bone. As an example, a veterinary surgeon may perform a technique known as a tibial plateau leveling osteotomy to remedy problems caused by a weakened or ruptured cranial cruciate ligament in the leg of a dog. When the cranial cruciate ligament of a dog is damaged, the tibia may move forward relative to the femur when the leg is loaded. This forward motion, known as tibial thrust, may cause more severe injury to the dog""s leg in the form of soft tissue (medial meniscus) impingement. The forward motion can occur because the tibial plateau, or the region of the proximal end of the tibia that contacts the femur, meets the femur at a nonperpendicular angle relative to the direction of the force the tibia exerts against the femur when the leg is loaded. The tibial plateau leveling osteotomy procedure is used to change the angle at which the tibial plateau contacts the femur to be more perpendicular to the direction of this force. In the procedure, a curvilinear cut is made in the proximal region of the tibia to free a portion of the tibia, including the tibial plateau region, from the rest of the bone. This portion may then be rotated along the curvilinear cut to change the angle at which the tibial plateau meets the femur. After the angle is changed to the desired angle, the bone portion is fixed to the rest of the tibia by conventional means.
Before performing an osteotomy procedure, a physician or veterinarian generally must explain the various aspects of the procedure to the patient or pet owner. For example, the doctor must explain the mechanics of the injured joint, and why the osteotomy is necessary to change the joint structure to fix the joint. The doctor must also explain how the osteotomy is performed, and why the joint will perform better after the surgery. Several methods may be used to convey this information to the patient. First, the doctor may simply talk to the patient. However, many people lack the physiological knowledge or training necessary to understand a discussion of bone mechanics and surgeries, even if the doctor describes the procedure in lay terms. Furthermore, a doctor often needs to use a relatively large quantity of unwieldy language to explain even simple procedures. Thus, a doctor who verbally describes a procedure runs the risk that a patient or pet owner will not understand all aspects of the procedure.
A doctor may also use some sort of visual aid to show the patient or pet owner how the procedure is to be performed. For example, a doctor may make or use two-dimensional illustrations of the joint before and after the surgery is performed to illustrate the procedure. Verbal descriptions combined with illustrations are superior to verbal descriptions alone for several reasons. First, a doctor may convey with a single illustration a complex idea that may be difficult to describe verbally. Also, the doctor may point to the illustration while describing a particular aspect of the joint or surgery to show the patient exactly what is being discussed. If the doctor wants to describe changes in the structure or performance of the joint caused by the surgery, the doctor may use separate illustrations to show the joint structure and mechanics before and after each step in the surgery. Though this method may make the description of the surgery somewhat easier for the patient to understand, it still presents difficulties. Most significantly, it is difficult to represent movement with illustrations. Separate illustrations may show the position of a bone before and after a movement, but the illustrations themselves do not represent the actual movement of the bone between the two positions. Thus, even with the use of two-dimensional illustrations, it remains difficult to explain in a simple manner exactly how the changes in bone structure alter the joint mechanics.
Rather than using two-dimensional illustrations to explain a surgical procedure, a doctor may also use a lifelike, three-dimensional skeletal model as a visual aid. Such models allow the motion of the joint to be demonstrated. However, due to the complexity of bone shapes and joint structures, a lay person may not be able to see subtle features in skeletal structure in these models. As an example, a lay person may have difficulty perceiving the angle at which the tibia meets the femur in a canine knee joint if shown a three-dimensional skeletal model of the joint. Also, these models may be fragile and difficult to transport. Thus, it would be desirable to have a simple apparatus or tool for illustrating the movement of a bone fragment during an osteotomy procedure, and for modeling the mechanics of a joint involved in the procedure both before and after the procedure.
One aspect of the present invention provides an apparatus for modeling a skeletal structure before and after a surgical procedure is performed on the structure. The apparatus comprises a base, the base including a generally planar surface, at least one bone member coupled to the base, the bone member representing a bone involved in the surgical procedure, and at least one bone portion movably coupled to the bone member, the bone portion representing a part of the bone involved in the surgical procedure that is repositioned in the surgical procedure from a preoperative position to a postoperative position. The bone portion may be selectively moved between a preoperative position, representing the position of the part of the bone before the surgical procedure is performed, and a postoperative position representing the position of the part of the bone after the surgical procedure is performed.
Another aspect of the present invention provides a tool for representing the mechanics of a skeletal joint before and after an osteotomy is performed on a bone of the joint. The tool comprises a base, the base including a generally planar surface, a first bone member coupled to the base substantially parallel to the base, the first bone member representing a first bone involved in the surgical procedure, and a second bone member movably coupled to the base substantially parallel to the base. The second bone member has opposing ends and represents a second bone involved in the surgical procedure. The second bone member is coupled to the first bone member such that one end of the second bone member is in movable contact with the first bone member to simulate the skeletal joint. The tool also includes a bone portion interposed between the first and second bone members, the bone portion representing a portion of one of the first and second bone members that is repositioned in the surgical procedure. The bone portion is movably coupled to one of the first and second bone members such that the bone portion may be selectively moved between a preoperative position, representing the position of the portion before the surgical procedure is performed, and a postoperative position, representing the position of the portion after the surgical procedure is performed. Movement of the joint before the performance of the surgical procedure may be represented by placing the bone portion in the preoperative position and moving the second bone member with respect to the base, and movement of the joint after the performance of the surgical procedure may be represented by placing the bone portion in the postoperative position and moving the second bone member with respect to the base.
Yet another aspect of the present invention provides a model for demonstrating tibial thrust in a canine knee joint before and after a tibial plateau leveling osteotomy procedure. The model comprises a base, including a generally planar surface, a femur member coupled to base, a foot member including an ankle portion and a heel portion, the foot member movably coupled to base at the heel portion, and a tibia member having opposing ends, the tibia member including a tibial plateau portion movably coupled to tibia member at one end of the tibia member. The tibia member extends between the foot member and the femur member such that the tibia member contacts the femur member at the tibial plateau portion to simulate a knee joint, and the tibia member is pivotally coupled to the ankle portion of the foot member at the other end to simulate an ankle joint. The tibial plateau portion may be moved between at least one preoperative position, wherein the angle of the tibial plateau portion relative to the femur member permits the tibial plateau portion to move in a forward direction relative to the femur member when the foot member is urged toward the tibia member, and at least one postoperative position, wherein the angle of the tibial plateau portion relative to the femur member prevents the tibial plateau portion from moving relative to the femur member when the foot member is urged toward the tibia member.